1. Field of the Invention
The invention generally relates to an apparatus and method for diagnostically testing the circuitry of a device. More particularly, the present invention relates to an apparatus and method for determining the location of a response within the circuitry of a device and/or for tracing the connectivity of the circuitry of a device.
2. Description of the Related Art
Physical fault isolation techniques can be used to image an integrated circuit (IC), and possibly provide information about its operation. These techniques are often used in conjunction with an IC tester to control the state and operation of the IC. IC testers can condition and exercise an IC by generating test pattern signals selected to test for a particular response or to test a particular connectivity path in the circuitry of an IC, when the IC circuitry is stimulated with an applied energy. The tester repeatedly inputs the test pattern signals into input pins of the IC and remotely monitors the resulting pass/fail output signals at the output pins of the IC. One such IC fault isolation technique is Laser Scanning Microscopy (LSM) soft response analysis. LSM analysis can be performed on an IC that is being operated cyclically. The IC is biased at a point between passing operation and failing operation. Specific points in the LSM image can be linked to a change in the pass/fail criteria determined at the tester. This technique is specifically applicable to behaviors of an IC that are functions of temperature, voltage or timing. This approach relies on a ‘local’ stimulus (i.e., a laser) and uses a remote detector (i.e., a tester) to evaluate the pass/fail status of the device at one or more of its output pins. A related method is known as Laser Asissted Device Alteration (LADA).
Other laser-based IC fault isolation techniques include, Thermal Induced Voltage Alteration (TIVA) and Light Induced Voltage Alteration (LIVA). TIVA and LIVA techniques use changes in the power demands of an IC measured at a power or ground pin to identify when the heat or light, respectively, from a laser has activated or altered a response or circuit.
Another class of fault isolation techniques is used for measuring electrical activity in operating integrated circuits. This group may include electron beam probing or Electron Beam Test (EBT), Laser Voltage Probing (LVP), magnetic field or magnetic force microscopy, Photon Emission Microscopy (PEM), Time Resolved Emission (TRE), and Picosecond Imaging Circuit Analysis (PICA). These methods measure one or more parameters such as electric field, magnetic field, or photon emission that may be associated with the electrical voltage or current on a conductor in the integrated circuit.